• 전력전자학회논문지
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• 제20권2호
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• pp.160-166
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• 2015

This study proposes an improved cell balancing circuit for fast equalization among lithium-ion (Li-ion) batteries. A simple voltage sensorless charge balancing circuit has been proposed in the past. This cell balancing circuit automatically transfers energy from high-to low-voltage battery cells. However, the circuit requires a switch with low on-resistance because the balancing speed is limited by the on-resistance of the switch. Balancing speed decreases as the voltage difference among the battery cells decrease. In this study, the balancing speed of the cell balancing circuit is enhanced by using the auxiliary circuit, which boosts the balancing current. The charging current is determined by the nominal battery cell voltage and thus, the balancing speed is almost constant despite the very small voltage differences among the batteries. Simulation results are provided to verify the validity of the proposed cell balancing circuit.

• 전력전자학회논문지
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• 제24권4호
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• pp.279-285
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• 2019

This study proposes an enhanced switching pattern that can improve energy transfer efficiency in an active cell-balancing circuit using a multiwinding transformer. This balancing circuit performs cell balancing by transferring energy stored in a specific cell with high energy to another cell containing low energy through a multiwinding transformer. The circuit operates in flyback and buck-boost modes in accordance with the energy transfer path. In the conventional flyback mode, the leakage inductance of the transformer and the stray inductance component of winding can transfer energy to an undesired path during the balancing operation. This case results in cell imbalance during the cell-balancing process, which reduces the energy transfer efficiency. An enhanced switching pattern that can effectively perform cell balancing by minimizing the amount of energy transferred to the nontarget cells due to the leakage inductance components in the flyback mode is proposed. Energy transfer efficiency and balancing speed can be significantly improved using the proposed switching pattern compared with that using the conventional switching pattern. The performance improvements are verified by experiments using a 1 W prototype cell-balancing circuit.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1812-1820
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• 2017

This paper analyzes a symmetric active cell balancer for a battery management system. The considered cell balancer uses a forward converter in which the circuit structure is symmetric. This cell-balancing method uses fewer switches and is simpler than the previously proposed active cell-balancing circuits. Active power switches of this cell-balancing circuit operate simultaneously with the same pulse width modulation signals. Therefore, this cell-balancing circuit requires less time to be balanced than a previous bidirectional-forward-converter-based cell balancer. This paper analyzes the operational principles and modes of this cell balancer with computer-based circuit simulation results as well as experimental results in which each unbalanced cell is equalized with this cell balancer. The maximum power transfer efficiency of the investigated cell balancer was 87.5% from the experimental results. In addition to the experimental and analytical results, this paper presents the performance of this symmetric active cell-balancing method.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 추계학술대회 논문집
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• pp.7-8
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• 2015

In this paper a cell-to-cell fast charge balancing circuit for the Lithium-Ion battery module is proposed. In the proposed topology the energy in a high voltage cell is transferred directly to a low voltage cell through the operation of the dc-dc converter. Furthermore, the charge balancing can be performed regardless of the battery operation whether it is being charged, discharged or relaxed. The monitoring circuit composed of a DSP and a battery monitoring IC is designed to monitor the cell voltage and detect the inferior cell thereby protecting the battery module from failure. In order to demonstrate the performance of the proposed topology, a prototype circuit was designed and applied to 12 Lithium-Ion battery module. It has been verified with the experiments that the charge equalization time of the proposed method was shorter compared with those of other methods.

• 전력전자학회논문지
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• 제23권4호
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• pp.247-255
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• 2018

This paper proposes a transformer design of a direct cell-to-cell active cell balancing circuit with a multi-winding transformer for battery management system (BMS) applications. The coupling coefficient of the multi-winding transformer and the output capacitance of MOSFETs significantly affect the balancing current transfer efficiency of the cell balancing operation. During the operation, the multi-winding transformer stores the energy charged in a specific source cell and subsequently transfers this energy to the target cell. However, the leakage inductance of the multi-winding transformer and the output capacitance of the MOSFET induce an abnormal energy transfer to the non-target cells, thereby degrading the transfer efficiency of the balancing current in each cell balancing operation. The impacts of the balancing current transfer efficiency deterioration are analyzed and a transformer design methodology that considers the coupling coefficient is proposed to enhance the transfer efficiency of the balancing current. The efficiency improvements resulting from the selection of an appropriate coupling coefficient are verified by conducting a simulation and experiment with a 1 W prototype cell balancing circuit.

• 전력전자학회논문지
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• 제20권5호
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• pp.389-394
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• 2015

This paper proposes a series-connected power conversion system that integrates a photovoltaic power conditioner and a charge-balancing circuit. In conventional methods, a photovoltaic power conditioner and a cell-balancing circuit are needed for photovoltaic systems with energy storage devices, which results in a complex configuration and high cost. To overcome these problems, a series-connected DC-DC power conditioning system that integrates a photovoltaic power conditioner with a charge-balancing circuit is proposed. During the generation, the system operates as power conditioner only, whereas it operates as a cell balancing circuit during the rest time. For the analysis, the operating principle of the circuit and the controller design are done by PSIM simulation. For verification, a hardware prototype with 48-W photovoltaic modules has been implemented. Results verified that the modularized photovoltaic power conversion system with a series-connected storage successfully works with the proposed method.

• 한국정보전자통신기술학회논문지
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• 제11권6호
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• pp.732-741
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• 2018

여러 배터리 셀을 직렬로 연결해서 사용하는 BMS에서 사용 가능 용량을 최대화시키기 위하여 각 셀의 전압을 같도록 맞춰주는 셀 밸런싱 기술이 필요하다. 다중 권선 변압기를 사용하는 능동 셀 밸런싱 회로에서 셀 간 직접적 (direct cell-to-cell)으로 에너지를 전달하는 밸런싱 회로는 PMOS 스위치와 NMOS 스위치를 구동하기 위한 게이트 구동 칩은 PMOS 스위치와 NMOS 스위치 개수 만큼 TLP2748 포토커플러(photocoupler)와 TLP2745 포토커플러가 필요하므로 원가가 증가하고 집적도가 떨어진다. 그래서 본 논문에서는 포토커플러를 사용하여 PMOS와 NMOS 스위칭소자를 구동하는 대신 70V BCD 공정기반의 PMOS 게이트 구동회로와 NMOS 게이트 구동회로, 스위칭 시간이 개선된 PMOS 게이트 구동회로와 NMOS 게이트 구동회로를 제안하였다. 스위칭 시간이 개선된 PMOS 게이트 구동 스위치의 ${\Delta}t$는 8.9ns이고, NMOS 게이트 구동 스위치의 ${\Delta}t$는 9.9ns로 양호한 결과를 얻었다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 전력전자학술대회 논문집
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• pp.401-402
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• 2015

In this paper a direct cell-to-cell charge balancing circuit which can transfer the charge from any cell to any cell in the battery string is introduced. In the proposed topology the energy in the high voltage cell is transferred to the low voltage cell through the simple operation of a dc-dc converter to get fast equalization. Furthermore, the charge equalization can be performed regardless of the battery module operation whether it is being charged, discharged or relaxed. The monitoring circuit composed of a DSP and a battery monitoring IC is designed to monitor the cell voltage and protect the battery. In order to demonstrate the advantages of the proposed topology, a prototype circuit was designed and applied to 12 Lithium-Ion battery module. It has been verified with the experiments that the charge equalization time of the proposed method was shortest compared with those of other methods.

• 센서학회지
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• 제21권5호
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• pp.379-384
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• 2012

This paper presents the power source of wireless sensor node (WSN) using supercapacitors and a solar cell. Supercapacitors have high lifetime cycling compared to that of batteries. Supercapacitors are connected in series to achieve higher voltage and a voltage balancing circuit is required to ensure that no individual cell goes overvoltage. We employ an active balancing circuit that draws minimal current by using transistors. A diode is connected in series with each supercapacitor. A new balancing circuit that equalize the cells-voltage reduces energy consumption of supercapacitors. Voltage of operating WSN is applied 2.2-3.3V by DC/DC converter and supercapacitor voltage 2.2-5.1V. Maximum operating time of wireless sensor node is about 16 hours in full charging.

• 전력전자학회논문지
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• 제21권4호
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• pp.335-342
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• 2016

This paper proposes an energy storage-assisted, series-connected module-integrated power conversion system that integrates a photovoltaic power conditioner and a charge balancing circuit. In conventional methods, a photovoltaic power conditioner and a cell-balancing circuit are needed for photovoltaic systems with energy storage devices, but they cause a complex configuration and high cost. Moreover, an imbalanced output voltage of the module-integrated converter for PV panels can be a result of partial shading. Partial shading can lead to the fault condition of the boost converter in shaded modules and high voltage stresses on the devices in other modules. To overcome these problems, a bidirectional buck-boost converter with an integrated magnetic device operating for a charge-balancing circuit is proposed. The proposed circuit has multiple secondary rectifiers with inductors sharing a single magnetic core, which works as an inductor for the main bidirectional charger/discharger of the energy storage. The secondary rectifiers operate as a cell-balancing circuit for both energy storage and the series-connected multiple outputs of the module-integrated converter. The operating principle of the cell-balancing power conversion circuit and the power stage design are presented and validated by PSIM simulation for analysis. A hardware prototype with equivalent photovoltaic modules is implemented for verification. The results verify that the modularized photovoltaic power conversion system in the output series with an energy storage successfully works with the proposed low-cost bidirectional buck-boost converter comprising a single magnetic device.